"Going forward now these girls are going to have to find a way of healing without a sense of justice," said Dr. Linda Papadopoulos, a U.K.-based psychologist and author. "We want the sense of justice when we heal. Sometimes we have to heal without it, and sadly that is what they will have to do."

She added: "He decided his fate, something they were never ever ever able to do for themselves. He had ultimate control. To some extent this was in a way his last slap to their faces -- 'I’ve got this over you'."

Addressing Castro in court, Knight said: "Days never got shorter. Days turned into nights, nights turned into days ... Years turned into an eternity. I spent 11 years in hell, now your hell is just beginning."

Castro's death could well rob Knight, DeJesus and Berry of the feeling that the former bus driver was paying for his crimes, Papadopoulous added.

"They very literally had a sentence dealt out to them ... They were literally, metaphorically, in every way imprisoned and held captive," Papadopoulos said. "The idea that he did this on his terms again is going to make them, at least to some extent, to feel cheated."

Survivors of such experiences may also feel great grief, said Eva Usadi, a New York City-based therapist specializing in first responder and combat trauma.

"The grief comes from there being no real justice," she said. "That’s what victims want even when the perpetrators go to jail for all their lives. But, on some level, there is no way to regain what’s been truly lost, which is innocence, a sense of the world being safe. And so this produces deep grief."

While Castro’s death may make his victims anger and grief, they may also feel relief, according to Dr. Nihara Krause, a British clinical psychologist who specializes in the effects of trauma.

“I think a lot of it just depends on the person and on their coping techniques,” she said. It could feel like “a huge positive in terms of an immediate relief … Sometimes it can positively make people free to remember without threat."

Krause advised survivors of this sort of trauma to “use every strategy to get it out. Write down whatever you’re remembering or express it to somebody."

She added: "But most importantly, remind yourself that whatever you’re thinking of are memories, they’re not real – that’s the most important thing. That’s part of trauma, you tend to experience it as if it were real. They are memories, no more than that.”